fix 923 (#927)

Co-authored-by: Salma <[email protected]>

Author: salmaahhmed

ios/Classes/FlutterDownloaderPlugin.m

@@ -370,7 +370,7 @@ - (NSURL*)fileUrlOf:(NSString*)taskId taskInfo:(NSDictionary*)taskInfo downloadT
 
 - (NSString *)sanitizeFilename:(nullable NSString *)filename {
     // Define a list of allowed characters for filenames
-    NSCharacterSet *allowedCharacters = [[NSCharacterSet characterSetWithCharactersInString:@"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-_.() "] invertedSet];
+    NSCharacterSet *allowedCharacters = [NSCharacterSet characterSetWithCharactersInString:@"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-_.() "];
 
     if (filename == nil || [filename isEqual:[NSNull null]] || [filename isEqualToString:@""]) {
            NSString *defaultFilename = @"default_filename";